Merge branch 'pw/rebase-keep-base-fixes'

"git rebase --keep-base" used to discard the commits that are
already cherry-picked to the upstream, even when "keep-base" meant
that the base, on top of which the history is being rebuilt, does
not yet include these cherry-picked commits.  The --keep-base
option now implies --reapply-cherry-picks and --no-fork-point
options.

* pw/rebase-keep-base-fixes:
  rebase --keep-base: imply --no-fork-point
  rebase --keep-base: imply --reapply-cherry-picks
  rebase: factor out branch_base calculation
  rebase: rename merge_base to branch_base
  rebase: store orig_head as a commit
  rebase: be stricter when reading state files containing oids
  t3416: set $EDITOR in subshell
  t3416: tighten two tests

6 files changed, 172 insertions, 89 deletions

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 9cb8931c7ac..f9675bd24e6 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -218,12 +218,14 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 	merge base of `<upstream>` and `<branch>`. Running
 	`git rebase --keep-base <upstream> <branch>` is equivalent to
 	running
-	`git rebase --onto <upstream>...<branch> <upstream> <branch>`.
+	`git rebase --reapply-cherry-picks --no-fork-point --onto <upstream>...<branch> <upstream> <branch>`.
 +
 This option is useful in the case where one is developing a feature on
 top of an upstream branch. While the feature is being worked on, the
 upstream branch may advance and it may not be the best idea to keep
-rebasing on top of the upstream but to keep the base commit as-is.
+rebasing on top of the upstream but to keep the base commit as-is. As
+the base commit is unchanged this option implies `--reapply-cherry-picks`
+to avoid losing commits.
 +
 Although both this option and `--fork-point` find the merge base between
 `<upstream>` and `<branch>`, this option uses the merge base as the _starting
@@ -278,7 +280,8 @@ See also INCOMPATIBLE OPTIONS below.
 Note that commits which start empty are kept (unless `--no-keep-empty`
 is specified), and commits which are clean cherry-picks (as determined
 by `git log --cherry-mark ...`) are detected and dropped as a
-preliminary step (unless `--reapply-cherry-picks` is passed).
+preliminary step (unless `--reapply-cherry-picks` or `--keep-base` is
+passed).
 +
 See also INCOMPATIBLE OPTIONS below.
 
@@ -311,13 +314,16 @@ See also INCOMPATIBLE OPTIONS below.
 	upstream changes, the behavior towards them is controlled by
 	the `--empty` flag.)
 +
-By default (or if `--no-reapply-cherry-picks` is given), these commits
-will be automatically dropped.  Because this necessitates reading all
-upstream commits, this can be expensive in repos with a large number
-of upstream commits that need to be read.  When using the 'merge'
-backend, warnings will be issued for each dropped commit (unless
-`--quiet` is given). Advice will also be issued unless
-`advice.skippedCherryPicks` is set to false (see linkgit:git-config[1]).
+
+In the absence of `--keep-base` (or if `--no-reapply-cherry-picks` is
+given), these commits will be automatically dropped.  Because this
+necessitates reading all upstream commits, this can be expensive in
+repositories with a large number of upstream commits that need to be
+read. When using the 'merge' backend, warnings will be issued for each
+dropped commit (unless `--quiet` is given). Advice will also be issued
+unless `advice.skippedCherryPicks` is set to false (see
+linkgit:git-config[1]).
+
 +
 `--reapply-cherry-picks` allows rebase to forgo reading all upstream
 commits, potentially improving performance.
@@ -443,9 +449,9 @@ When `--fork-point` is active, 'fork_point' will be used instead of
 <branch>` command (see linkgit:git-merge-base[1]).  If 'fork_point'
 ends up being empty, the `<upstream>` will be used as a fallback.
 +
-If `<upstream>` is given on the command line, then the default is
-`--no-fork-point`, otherwise the default is `--fork-point`. See also
-`rebase.forkpoint` in linkgit:git-config[1].
+If `<upstream>` or `--keep-base` is given on the command line, then
+the default is `--no-fork-point`, otherwise the default is
+`--fork-point`. See also `rebase.forkpoint` in linkgit:git-config[1].
 +
 If your branch was based on `<upstream>` but `<upstream>` was rewound and
 your branch contains commits which were dropped, this option can be used
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 56e4214b441..b9164a30bff 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -68,7 +68,7 @@ struct rebase_options {
 	const char *upstream_name;
 	const char *upstream_arg;
 	char *head_name;
-	struct object_id orig_head;
+	struct commit *orig_head;
 	struct commit *onto;
 	const char *onto_name;
 	const char *revisions;
@@ -261,13 +261,13 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 	struct replay_opts replay = get_replay_opts(opts);
 	struct string_list commands = STRING_LIST_INIT_DUP;
 
-	if (get_revision_ranges(opts->upstream, opts->onto, &opts->orig_head,
+	if (get_revision_ranges(opts->upstream, opts->onto, &opts->orig_head->object.oid,
 				&revisions, &shortrevisions))
 		return -1;
 
 	if (init_basic_state(&replay,
 			     opts->head_name ? opts->head_name : "detached HEAD",
-			     opts->onto, &opts->orig_head)) {
+			     opts->onto, &opts->orig_head->object.oid)) {
 		free(revisions);
 		free(shortrevisions);
 
@@ -298,9 +298,8 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 		split_exec_commands(opts->cmd, &commands);
 		ret = complete_action(the_repository, &replay, flags,
 			shortrevisions, opts->onto_name, opts->onto,
-			&opts->orig_head, &commands, opts->autosquash,
-			opts->update_refs,
-			&todo_list);
+			&opts->orig_head->object.oid, &commands,
+			opts->autosquash, opts->update_refs, &todo_list);
 	}
 
 	string_list_clear(&commands, 0);
@@ -431,9 +430,9 @@ static int read_basic_state(struct rebase_options *opts)
 	opts->head_name = starts_with(head_name.buf, "refs/") ?
 		xstrdup(head_name.buf) : NULL;
 	strbuf_release(&head_name);
-	if (get_oid(buf.buf, &oid))
-		return error(_("could not get 'onto': '%s'"), buf.buf);
-	opts->onto = lookup_commit_or_die(&oid, buf.buf);
+	if (get_oid_hex(buf.buf, &oid) ||
+	    !(opts->onto = lookup_commit_object(the_repository, &oid)))
+		return error(_("invalid onto: '%s'"), buf.buf);
 
 	/*
 	 * We always write to orig-head, but interactive rebase used to write to
@@ -448,7 +447,8 @@ static int read_basic_state(struct rebase_options *opts)
 	} else if (!read_oneliner(&buf, state_dir_path("head", opts),
 				  READ_ONELINER_WARN_MISSING))
 		return -1;
-	if (get_oid(buf.buf, &opts->orig_head))
+	if (get_oid_hex(buf.buf, &oid) ||
+	    !(opts->orig_head = lookup_commit_object(the_repository, &oid)))
 		return error(_("invalid orig-head: '%s'"), buf.buf);
 
 	if (file_exists(state_dir_path("quiet", opts)))
@@ -517,7 +517,7 @@ static int rebase_write_basic_state(struct rebase_options *opts)
 	write_file(state_dir_path("onto", opts), "%s",
 		   opts->onto ? oid_to_hex(&opts->onto->object.oid) : "");
 	write_file(state_dir_path("orig-head", opts), "%s",
-		   oid_to_hex(&opts->orig_head));
+		   oid_to_hex(&opts->orig_head->object.oid));
 	if (!(opts->flags & REBASE_NO_QUIET))
 		write_file(state_dir_path("quiet", opts), "%s", "");
 	if (opts->flags & REBASE_VERBOSE)
@@ -646,7 +646,7 @@ static int run_am(struct rebase_options *opts)
 			       /* this is now equivalent to !opts->upstream */
 			       &opts->onto->object.oid :
 			       &opts->upstream->object.oid),
-		    oid_to_hex(&opts->orig_head));
+		    oid_to_hex(&opts->orig_head->object.oid));
 
 	rebased_patches = xstrdup(git_path("rebased-patches"));
 	format_patch.out = open(rebased_patches,
@@ -680,7 +680,7 @@ static int run_am(struct rebase_options *opts)
 		free(rebased_patches);
 		strvec_clear(&am.args);
 
-		ropts.oid = &opts->orig_head;
+		ropts.oid = &opts->orig_head->object.oid;
 		ropts.branch = opts->head_name;
 		ropts.default_reflog_action = DEFAULT_REFLOG_ACTION;
 		reset_head(the_repository, &ropts);
@@ -833,7 +833,7 @@ static int checkout_up_to_date(struct rebase_options *options)
 	strbuf_addf(&buf, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT),
 		    options->switch_to);
-	ropts.oid = &options->orig_head;
+	ropts.oid = &options->orig_head->object.oid;
 	ropts.branch = options->head_name;
 	ropts.flags = RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
 	if (!ropts.branch)
@@ -866,32 +866,23 @@ static int is_linear_history(struct commit *from, struct commit *to)
 
 static int can_fast_forward(struct commit *onto, struct commit *upstream,
 			    struct commit *restrict_revision,
-			    struct object_id *head_oid, struct object_id *merge_base)
+			    struct commit *head, struct object_id *branch_base)
 {
-	struct commit *head = lookup_commit(the_repository, head_oid);
 	struct commit_list *merge_bases = NULL;
 	int res = 0;
 
-	if (!head)
-		goto done;
+	if (is_null_oid(branch_base))
+		goto done; /* fill_branch_base() found multiple merge bases */
 
-	merge_bases = get_merge_bases(onto, head);
-	if (!merge_bases || merge_bases->next) {
-		oidcpy(merge_base, null_oid());
+	if (!oideq(branch_base, &onto->object.oid))
 		goto done;
-	}
 
-	oidcpy(merge_base, &merge_bases->item->object.oid);
-	if (!oideq(merge_base, &onto->object.oid))
-		goto done;
-
-	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, branch_base))
 		goto done;
 
 	if (!upstream)
 		goto done;
 
-	free_commit_list(merge_bases);
 	merge_bases = get_merge_bases(upstream, head);
 	if (!merge_bases || merge_bases->next)
 		goto done;
@@ -906,6 +897,20 @@ done:
 	return res && is_linear_history(onto, head);
 }
 
+static void fill_branch_base(struct rebase_options *options,
+			    struct object_id *branch_base)
+{
+	struct commit_list *merge_bases = NULL;
+
+	merge_bases = get_merge_bases(options->onto, options->orig_head);
+	if (!merge_bases || merge_bases->next)
+		oidcpy(branch_base, null_oid());
+	else
+		oidcpy(branch_base, &merge_bases->item->object.oid);
+
+	free_commit_list(merge_bases);
+}
+
 static int parse_opt_am(const struct option *opt, const char *arg, int unset)
 {
 	struct rebase_options *opts = opt->value;
@@ -1039,7 +1044,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
 	struct strbuf buf = STRBUF_INIT;
-	struct object_id merge_base;
+	struct object_id branch_base;
 	int ignore_whitespace = 0;
 	enum action action = ACTION_NONE;
 	const char *gpg_sign = NULL;
@@ -1175,6 +1180,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	prepare_repo_settings(the_repository);
 	the_repository->settings.command_requires_full_index = 0;
 
+	options.reapply_cherry_picks = -1;
 	options.allow_empty_message = 1;
 	git_config(rebase_config, &options);
 	/* options.gpg_sign_opt will be either "-S" or NULL */
@@ -1233,7 +1239,19 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			die(_("options '%s' and '%s' cannot be used together"), "--keep-base", "--onto");
 		if (options.root)
 			die(_("options '%s' and '%s' cannot be used together"), "--keep-base", "--root");
+		/*
+		 * --keep-base defaults to --no-fork-point to keep the
+		 * base the same.
+		 */
+		if (options.fork_point < 0)
+			options.fork_point = 0;
 	}
+	/*
+	 * --keep-base defaults to --reapply-cherry-picks to avoid losing
+	 * commits when using this option.
+	 */
+	if (options.reapply_cherry_picks < 0)
+		options.reapply_cherry_picks = keep_base;
 
 	if (options.root && options.fork_point > 0)
 		die(_("options '%s' and '%s' cannot be used together"), "--root", "--fork-point");
@@ -1312,13 +1330,13 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 		if (read_basic_state(&options))
 			exit(1);
-		ropts.oid = &options.orig_head;
+		ropts.oid = &options.orig_head->object.oid;
 		ropts.branch = options.head_name;
 		ropts.flags = RESET_HEAD_HARD;
 		ropts.default_reflog_action = DEFAULT_REFLOG_ACTION;
 		if (reset_head(the_repository, &ropts) < 0)
 			die(_("could not move back to %s"),
-			    oid_to_hex(&options.orig_head));
+			    oid_to_hex(&options.orig_head->object.oid));
 		remove_branch_state(the_repository, 0);
 		ret = finish_rebase(&options);
 		goto cleanup;
@@ -1410,7 +1428,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (options.empty != EMPTY_UNSPECIFIED)
 		imply_merge(&options, "--empty");
 
-	if (options.reapply_cherry_picks)
+	/*
+	 * --keep-base implements --reapply-cherry-picks by altering upstream so
+	 * it works with both backends.
+	 */
+	if (options.reapply_cherry_picks && !keep_base)
 		imply_merge(&options, "--reapply-cherry-picks");
 
 	if (gpg_sign)
@@ -1604,25 +1626,27 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 */
 	if (argc == 1) {
 		/* Is it "rebase other branchname" or "rebase other commit"? */
+		struct object_id branch_oid;
 		branch_name = argv[0];
 		options.switch_to = argv[0];
 
 		/* Is it a local branch? */
 		strbuf_reset(&buf);
 		strbuf_addf(&buf, "refs/heads/%s", branch_name);
-		if (!read_ref(buf.buf, &options.orig_head)) {
+		if (!read_ref(buf.buf, &branch_oid)) {
 			die_if_checked_out(buf.buf, 1);
 			options.head_name = xstrdup(buf.buf);
+			options.orig_head =
+				lookup_commit_object(the_repository,
+						     &branch_oid);
 		/* If not is it a valid ref (branch or commit)? */
 		} else {
-			struct commit *commit =
+			options.orig_head =
 				lookup_commit_reference_by_name(branch_name);
-			if (!commit)
-				die(_("no such branch/commit '%s'"),
-				    branch_name);
-			oidcpy(&options.orig_head, &commit->object.oid);
 			options.head_name = NULL;
 		}
+		if (!options.orig_head)
+			die(_("no such branch/commit '%s'"), branch_name);
 	} else if (argc == 0) {
 		/* Do not need to switch branches, we are already on it. */
 		options.head_name =
@@ -1639,8 +1663,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			FREE_AND_NULL(options.head_name);
 			branch_name = "HEAD";
 		}
-		if (get_oid("HEAD", &options.orig_head))
-			die(_("Could not resolve HEAD to a revision"));
+		options.orig_head = lookup_commit_reference_by_name("HEAD");
+		if (!options.orig_head)
+			die(_("Could not resolve HEAD to a commit"));
 	} else
 		BUG("unexpected number of arguments left to parse");
 
@@ -1654,7 +1679,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+		if (get_oid_mb(options.onto_name, &branch_base) < 0) {
 			if (keep_base)
 				die(_("'%s': need exactly one merge base with branch"),
 				    options.upstream_name);
@@ -1662,7 +1687,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				die(_("'%s': need exactly one merge base"),
 				    options.onto_name);
 		}
-		options.onto = lookup_commit_or_die(&merge_base,
+		options.onto = lookup_commit_or_die(&branch_base,
 						    options.onto_name);
 	} else {
 		options.onto =
@@ -1670,15 +1695,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		if (!options.onto)
 			die(_("Does not point to a valid commit '%s'"),
 				options.onto_name);
+		fill_branch_base(&options, &branch_base);
 	}
 
-	if (options.fork_point > 0) {
-		struct commit *head =
-			lookup_commit_reference(the_repository,
-						&options.orig_head);
+	if (keep_base && options.reapply_cherry_picks)
+		options.upstream = options.onto;
+
+	if (options.fork_point > 0)
 		options.restrict_revision =
-			get_fork_point(options.upstream_name, head);
-	}
+			get_fork_point(options.upstream_name, options.orig_head);
 
 	if (repo_read_index(the_repository) < 0)
 		die(_("could not read index"));
@@ -1703,13 +1728,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * Check if we are already based on onto with linear history,
 	 * in which case we could fast-forward without replacing the commits
 	 * with new commits recreated by replaying their changes.
-	 *
-	 * Note that can_fast_forward() initializes merge_base, so we have to
-	 * call it before checking allow_preemptive_ff.
 	 */
-	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
-		    &options.orig_head, &merge_base) &&
-	    allow_preemptive_ff) {
+	if (allow_preemptive_ff &&
+	    can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+			     options.orig_head, &branch_base)) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
@@ -1750,12 +1772,12 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		struct diff_options opts;
 
 		if (options.flags & REBASE_VERBOSE) {
-			if (is_null_oid(&merge_base))
+			if (is_null_oid(&branch_base))
 				printf(_("Changes to %s:\n"),
 				       oid_to_hex(&options.onto->object.oid));
 			else
 				printf(_("Changes from %s to %s:\n"),
-				       oid_to_hex(&merge_base),
+				       oid_to_hex(&branch_base),
 				       oid_to_hex(&options.onto->object.oid));
 		}
 
@@ -1767,8 +1789,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 		opts.detect_rename = DIFF_DETECT_RENAME;
 		diff_setup_done(&opts);
-		diff_tree_oid(is_null_oid(&merge_base) ?
-			      the_hash_algo->empty_tree : &merge_base,
+		diff_tree_oid(is_null_oid(&branch_base) ?
+			      the_hash_algo->empty_tree : &branch_base,
 			      &options.onto->object.oid, "", &opts);
 		diffcore_std(&opts);
 		diff_flush(&opts);
@@ -1785,7 +1807,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
 	ropts.oid = &options.onto->object.oid;
-	ropts.orig_head = &options.orig_head,
+	ropts.orig_head = &options.orig_head->object.oid,
 	ropts.flags = RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 			RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
 	ropts.head_msg = msg.buf;
@@ -1799,7 +1821,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * we just fast-forwarded.
 	 */
 	strbuf_reset(&msg);
-	if (oideq(&merge_base, &options.orig_head)) {
+	if (oideq(&branch_base, &options.orig_head->object.oid)) {
 		printf(_("Fast-forwarded %s to %s.\n"),
 			branch_name, options.onto_name);
 		strbuf_addf(&msg, "rebase finished: %s onto %s",
@@ -1820,7 +1842,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		    (options.restrict_revision ?
 		     oid_to_hex(&options.restrict_revision->object.oid) :
 		     oid_to_hex(&options.upstream->object.oid)),
-		    oid_to_hex(&options.orig_head));
+		    oid_to_hex(&options.orig_head->object.oid));
 
 	options.revisions = revisions.buf;
 
diff --git a/commit.c b/commit.c
index 89b8efc6116..572301b80a2 100644
--- a/commit.c
+++ b/commit.c
@@ -59,6 +59,14 @@ struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref
 	return c;
 }
 
+struct commit *lookup_commit_object(struct repository *r,
+				    const struct object_id *oid)
+{
+	struct object *obj = parse_object(r, oid);
+	return obj ? object_as_type(obj, OBJ_COMMIT, 0) : NULL;
+
+}
+
 struct commit *lookup_commit(struct repository *r, const struct object_id *oid)
 {
 	struct object *obj = lookup_object(r, oid);
diff --git a/commit.h b/commit.h
index 21e4d25ce78..fa39202fa6b 100644
--- a/commit.h
+++ b/commit.h
@@ -64,6 +64,19 @@ enum decoration_type {
 void add_name_decoration(enum decoration_type type, const char *name, struct object *obj);
 const struct name_decoration *get_name_decoration(const struct object *obj);
 
+/*
+ * Look up commit named by "oid" respecting replacement objects.
+ * Returns NULL if "oid" is not a commit or does not exist.
+ */
+struct commit *lookup_commit_object(struct repository *r, const struct object_id *oid);
+
+/*
+ * Look up commit named by "oid" without replacement objects or
+ * checking for object existence. Returns the requested commit if it
+ * is found in the object cache, NULL if "oid" is in the object cache
+ * but is not a commit and a newly allocated unparsed commit object if
+ * "oid" is not in the object cache.
+ */
 struct commit *lookup_commit(struct repository *r, const struct object_id *oid);
 struct commit *lookup_commit_reference(struct repository *r,
 				       const struct object_id *oid);
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index 3e04802cb00..ea501f2b42b 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -79,8 +79,10 @@ test_expect_success 'rebase -i --onto main...topic' '
 	git reset --hard &&
 	git checkout topic &&
 	git reset --hard G &&
-	set_fake_editor &&
-	EXPECT_COUNT=1 git rebase -i --onto main...topic F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=1 git rebase -i --onto main...topic F
+	) &&
 	git rev-parse HEAD^1 >actual &&
 	git rev-parse C^0 >expect &&
 	test_cmp expect actual
@@ -90,20 +92,22 @@ test_expect_success 'rebase -i --onto main...' '
 	git reset --hard &&
 	git checkout topic &&
 	git reset --hard G &&
-	set_fake_editor &&
-	EXPECT_COUNT=1 git rebase -i --onto main... F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=1 git rebase -i --onto main... F
+	) &&
 	git rev-parse HEAD^1 >actual &&
 	git rev-parse C^0 >expect &&
 	test_cmp expect actual
 '
 
-test_expect_success 'rebase -i --onto main...side' '
+test_expect_success 'rebase --onto main...side requires a single merge-base' '
 	git reset --hard &&
 	git checkout side &&
 	git reset --hard K &&
 
-	set_fake_editor &&
-	test_must_fail git rebase -i --onto main...side J
+	test_must_fail git rebase -i --onto main...side J 2>err &&
+	grep "need exactly one merge base" err
 '
 
 test_expect_success 'rebase --keep-base --onto incompatible' '
@@ -156,8 +160,10 @@ test_expect_success 'rebase -i --keep-base main from topic' '
 	git checkout topic &&
 	git reset --hard G &&
 
-	set_fake_editor &&
-	EXPECT_COUNT=2 git rebase -i --keep-base main &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=2 git rebase -i --keep-base main
+	) &&
 	git rev-parse C >base.expect &&
 	git merge-base main HEAD >base.actual &&
 	test_cmp base.expect base.actual &&
@@ -171,8 +177,10 @@ test_expect_success 'rebase -i --keep-base main topic from main' '
 	git checkout main &&
 	git branch -f topic G &&
 
-	set_fake_editor &&
-	EXPECT_COUNT=2 git rebase -i --keep-base main topic &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=2 git rebase -i --keep-base main topic
+	) &&
 	git rev-parse C >base.expect &&
 	git merge-base main HEAD >base.actual &&
 	test_cmp base.expect base.actual &&
@@ -182,13 +190,39 @@ test_expect_success 'rebase -i --keep-base main topic from main' '
 	test_cmp expect actual
 '
 
-test_expect_success 'rebase -i --keep-base main from side' '
+test_expect_success 'rebase --keep-base requires a single merge base' '
 	git reset --hard &&
 	git checkout side &&
 	git reset --hard K &&
 
-	set_fake_editor &&
-	test_must_fail git rebase -i --keep-base main
+	test_must_fail git rebase -i --keep-base main 2>err &&
+	grep "need exactly one merge base with branch" err
+'
+
+test_expect_success 'rebase --keep-base keeps cherry picks' '
+	git checkout -f -B main E &&
+	git cherry-pick F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=2 git rebase -i --keep-base HEAD G
+	) &&
+	test_cmp_rev HEAD G
+'
+
+test_expect_success 'rebase --keep-base --no-reapply-cherry-picks' '
+	git checkout -f -B main E &&
+	git cherry-pick F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=1 git rebase -i --keep-base \
+					--no-reapply-cherry-picks HEAD G
+	) &&
+	test_cmp_rev HEAD^ C
+'
+
+# This must be the last test in this file
+test_expect_success '$EDITOR and friends are unchanged' '
+	test_editor_unchanged
 '
 
 test_done
diff --git a/t/t3431-rebase-fork-point.sh b/t/t3431-rebase-fork-point.sh
index 1d0b15380ed..70e81363569 100755
--- a/t/t3431-rebase-fork-point.sh
+++ b/t/t3431-rebase-fork-point.sh
@@ -50,7 +50,7 @@ test_rebase () {
 
 test_rebase 'G F E D B A'
 test_rebase 'G F D B A' --onto D
-test_rebase 'G F B A' --keep-base
+test_rebase 'G F C B A' --keep-base
 test_rebase 'G F C E D B A' --no-fork-point
 test_rebase 'G F C D B A' --no-fork-point --onto D
 test_rebase 'G F C B A' --no-fork-point --keep-base